1 day after people; The Soviet submarine K-129 still lies at the bottom of the Pacific Ocean. When it sank in 1968 it carried a payload of nuclear torpedoes and missiles. The missiles will explode if their cassings start to leak but as of now they are still keeping the ocean water out.
25 years after people, The casings of the torpedoes have become weak and begun leaking water. The torpedoes explode but the explosion is muted by the pressure of the ocean. The torpedo’s plutonium core is scattered over a small area and any sea creatures that come in contact with it die of radiation poisoning.